Shielded electret transducer and method of making the same

Abstract

An electret transducer including a pair of spaced electrodes, one electrode being connected to a preamplifier input, an insulator on the outer surface of the electrode connected to the preamplifier input, and a conductive layer on the other side of the insulator, whereby the conductive layer can be used to shield the electrode to reduce stray capacitance between it and other components of the transducer by connecting the conductive shield to the output of the preamplifier circuit for the transducer. Also disclosd is the use of a silicon backplate with an integrated circuit formed therein, an insulator layer thereon, a conductive layer thereon, and an electret layer thereon, the conductive layer being grounded during poling of the electret to protect the integrated circuit from damage.

What is claimed is: 
     
       1. An electret transducer and preamplifier combination comprising a pair of spaced electrodes, one said electrode being a flexible electrode so as to change the spacing between electrodes in response to force on said one electrode, the other said electrode being fixed,   an electret between said electrodes,   an insulator on the outer surface of the other said electrode,   a conductive layer on the other side of said insulator, said conductive layer being a silicon backplate on which said electret and insulator are supported, and     a preamplifier having near unity gain, said conductive layer being connected to the output of said preamplifier,   whereby said conductive layer can be used to shield said other electrode to reduce stray capacitance between said other electrode and other components of said transducer.   
     
     
       2. The transducer and preamplifier combination of claim 1 wherein said silicon backplate includes an amplifier circuit formed integrally therewith. 
     
     
       3. The transducer and preamplifier combination of claim 1 wherein said silicon backplate includes a peripheral rim, and said flexible electrode is attached at its periphery to said rim. 
     
     
       4. The transducer and preamplifier combination of claim 3 further comprising a conductive housing that is electrically connected to said flexible electrode. 
     
     
       5. An electret transducer and amplifier circuit comprising transistor having source, gate and drain nodes,   a pair of spaced electrodes, one said electrode being connected to said gate, another said electrode being connected to one of said drain and source, a said electrode being a flexible electrode so as to change the spacing between electrodes in response to force on said flexible electrode,   an electret between said electrodes, and   a conductive member spaced from the outer surface of said one electrode being connected to said gate, said conductive member being connected to the other of said drain and source.     
     
     
       6. The transducer and circuit of claim 5 wherein said conductive member is a silicon backplate, and further comprising an insulator layer on said backplate spacing said silicon backplate from said another said electrode. 
     
     
       7. The transducer and circuit of claim 6 wherein said transistor is a field affect transistor formed integrally with said silicon backplate. 
     
     
       8. The transducer and circuit of claim 7 wherein said silicon backplate includes a peripheral rim, and said flexible electrode is attached at its periphery to said rim. 
     
     
       9. The transducer and circuit of claim 8 further comprising a conductive housing that is electrically connected to said flexible electrode.